Fatty acids, in particular, those containing C6-C24 carbon atoms, are major components and precursors for a large variety of products such as soaps, detergents, fatty alcohols, cosmetics, pharmaceuticals, foods, lubricants, plasticizers etc. They can be used as a single component or a mixture of well-defined fatty acids. The main sources of their production are vegetable or natural oils and animal fats. Currently, fatty acids are mainly produced from the reaction of vegetable oils and/or animal fats with superheated steam at high temperatures and pressures (An Ullmann's Encyclopedia, Industrial Organic Chemicals: Starting Materials and Intermediates, Wiley-VCH, Weinheim, Germany, Vol. 4, Year 1999, pp. 2481-2532).
In the Colgate-Emery process, most widely employed, the reaction is conducted in a continuous, counter flow mode, in the absence of a catalyst, at a temperature of 250-330° C. and a pressure of 49-80 Kg/cm2 (H. L. Barnebey, The Journal of the American Oil Chemists' Society, Year 1948, pp. 95-99). This process is efficient and vegetable oil/fat splitting yields of 98% and above are obtained. However, its applicability to all kinds of vegetable oils and animal fats especially those containing conjugated double bonds and hydroxyl substituents in their fatty acid back bone (ca., castor oil, fish oil etc) is limited. At high temperatures, the damage of fatty acids resulting from oxidation, decomposition, dehydration, polymerization and polycondensation are the usual undesired side reactions. Their propensity increases exponentially with temperature. The by-products formed lead to deterioration in color and odour and to a reduced yield of distillate fatty acid (Russell L. Holliday, Jerry W. King, Gary R. List, Ind. Eng. Chem. Res. Year 1997, Vol. 36, pp. 932-935).
The Twitchell fat splitting process is a batch reaction process. It is not in much use at present. It operates at moderate temperatures (ca. 100° C.) and atmospheric pressure employing a homogeneous catalyst. Twitchell reagent comprises of hydrocarbons, oleic acid and concentrated sulphuric acid. This process needs longer contact times (12-24 hrs) than the Colgate-Emery process and fat splitting is 80-85% only (L. Hartman, The Journal of the American Oil Chemists' Society, Year 1953, pp. 349-350).
Fatty splitting via saponification is one of the oldest methods in practice. U.S. Pat. Nos. 6,646,146 B1 and 5,383,678 disclose such processes performed in the presence of a metal or alkaline earth metal catalyst. This process produces metal soaps. In order to convert it to fatty acids, the product needs to be acidified, which in turn results in significant amount of inorganic waste and hard water. The quality of glycerine by-product is low. Additional process steps are essential to convert this glycerol into pharmaceutical grade glycerine.
Enzymatic splitting of fat is a low energy process (35° C.) but requires long contact times (16 hrs to several days) (U.S. Pat. No. 6,933,139 B2; Warner M. Linfield, Dennis J. O'Brien, Samuel Serota and Robert A. Barauskas, JAOCS, Year 1984, Vol. 61, pp. 1067-1071). U.S. Pat. No. 6,258,575 B1 discloses a process employing immobilized enzymes as catalysts. While complete hydrolysis can be achieved, leaching of enzyme into the reaction mixture and long term stability of the catalyst are the common issues.
References may be made to US patent application 2006/0047131 A1 reports a process to split free fatty acids from glycerol by hydrolysis at 60° C. and atmospheric pressure, under down-flow condition, in a packed column reactor containing calcium and magnesium oxide stones.
Recently, biodiesel is produced from fatty acids. While biodiesel is conventionally manufactured via transesterification of vegetable oils with alcohols, this method, however, is only applicable to refine vegetable oils/fats or those with a low content of free fatty acids and water. In the case of high content of fatty acids and/or water, as found in crude oils/fats, waste-frying oil, and soap stocks, the yield of methyl esters (bio-diesel) is low since fatty acids and water inhibit the reaction. Therefore, a two-step preparation of bio-diesel fuel was introduced wherein in the first step the feed stock is hydrolyzed at sub-critical conditions to free fatty acids and in the second step fatty acids, thus, produced, are esterified with an alcohol at supercritical conditions to form fatty acid alkyl esters (biodiesel) (Dadan Kusdiana and Shiro Saka, Appl. Biochem. Biotech. Year 2004, Vol. 113-116, pp. 781).
References may be made to patent WO 2003087027 relates to a liquid phase process for hydrolyzing a fatty acid ester to its corresponding fatty acid at a temperature of between 200-350° C., more preferably 250-280° C. and at a pressure of between 2-100 bar, preferably 10-70 bar; wherein the method comprises the steps of contacting fatty acid ester (in the liquid phase) with water (molar ratio of the amount of water with respect to the amount of fatty acid ester is at least 1) in the presence of an acid catalyst selected from the group of zeolites, ion exchange resins and acid amorphous catalysts. The process is carried out as a continuous process or a batch process. In this process, in order to achieve reasonably high fatty acid yields the process needs to be operated above 250° C., at which temperatures oils containing conjugated double bonds and hydroxyl groups (e.g., castor oil, fish oil etc.) get damaged and form undesired products. Further, the examples included are for the hydrolysis of short chain fatty acid methyl esters, namely C8-C12, yielding maximum of 70% in a batch process as exemplified in example 1-5 and 7-9. Also, this application does not cite examples for fatty acid glycerides and long chain esters.
References may be made to U.S. Pat. No. 6,646,146, wherein liquid phase process for the direct hydrolysis of a fatty acid ester (6-20 carbon atoms) to the corresponding fatty acid and alcohol in the presence of a catalyst which is an oxide, alkoxide, hydroxide or a salt of an organic acid of a metal selected from Li, Zn, Sn, Al, Ba, Ca, Mg, Ti, and Zr, capable of forming a soap with a large hydration shell_at a temperature preferably 180-230° C.; and under pressure of 43.5-290 psi. The hydrolysis is carried out in the presence of 0.01 to 0.2 percent by weight of metal with respect to the weight of the ester, preferably 500-2000 ppm of metal has disclosed. Saponification and metal soaps formation would be an issue with this process.
References may be made to U.S. Pat. No. 2,458,170, wherein inventor claims the method of hydrolysing fats and fatty oils with water to fatty acids and glycerine, with the aid of heat and pressure, which comprises intimately contacting such fatty material with water by counter current flow, whereby the fatty material undergoes substantial hydrolysis with the formation of fatty acids and glycerine. The hydrolysis is carried in absence of catalyst whereby substantially complete aqueous hydrolysis of fats and fatty oils is achieved without catalyst contamination. At lower temperatures and pressures, longer periods are required for the reaction to reach an equilibrium point, and at equilibrium the hydrolysis is considerably less.
Hydrolysis of vegetable oils/fats is an endothermic reaction. The extent of hydrolysis increases with an increase in temperature. Further at higher temperatures, miscibility of water in lipid increases and thereby enhances the reaction rate. However, the major drawbacks of the high temperature process as stated above are: It is an energy intensive and costly process. It uses considerable amount of superheated steam as a reagent. It requires the use of large reactors made of expensive corrosive-resistant material. The quality of crude product is poor and requires additional process step to purify the products fatty acids and glycerol that escalate the cost of the overall manufacturing process.
References may be made to Journal “Ind. Eng. Chem. Res. Vol. 48, Year 2009, pp. 4757-4767”, wherein Ngaosuwan et al have reported the application solid acid catalysts—tungstated zirconia and Nation resin nanoparticles supported on mesoporous silica (SAC-13) for the hydrolysis of a model system tricaprylin. The reaction was conducted at atmospheric pressure and 110-150° C. in a semi batch reactor with continuous addition of water at low flow rates. This process suffers from major drawbacks such as catalyst has to be calcined before recycling and this process does not give over 90% conversions, especially in longer chains. Further, another drawback of this acid catalyst system is its deactivation in recycling studies.
In view of the above, it is desirable to have an efficient, economically beneficial, eco-friendly, catalytic, hydrolysis process of vegetable oils which operates at moderate temperatures and produces high purity free fatty acids and glycerine.
It would also definitely be advantageous to have a catalyst system that is easily recoverable and reusable and avoids formation of saponified compounds. The catalyst should also have features such that it is not leachable. The prior art catalysts suffer from a distinct disadvantage of inverse temperature-time relationship, where the temperature when raised to over 250 deg C. results in quicker processes, but is still energy intensive and also is unsuitable for the hydrolysis of temperature sensitive materials. Fatty acids with reactive groups (conjugated double bonds and hydroxyl groups such as those present in fish oil, castor oil etc.) are unstable at higher temperatures and will form undesirable tar products. The yield of by-product glycerol will also be lower at higher temperatures.
Another disadvantage of the prior art catalyst systems is that these are more hydrophilic; therefore do not facilitate adsorption of fatty oil molecules which can enhance rate of reaction at even lower temperatures.